Sow housings of the kind in question are used in planters where the seeds are sowed singulated one by one.
In that connection, there are requirements of capacity, simplicity to handle the machines and the sow precision that the machines deliver. In order to provide good conditions for the crops and the harvest, it is particularly required that the machines should sow the seeds at a great accuracy regarding the position of the seeds in depth and their mutual spacing. In addition, it is desirable that such an accuracy is obtained at as high a speed of motion as possible. U.S. Pat. No. 3,888,387 and U.S. Pat. No. 4,047,638 disclose planters having singulating discs. Such planters comprise seed metering devices, each one of which comprising a seed element in the form of a round seed disc, also called singulating disc, which is rotatable around a concentric seed metering shaft and provided with a plurality of through retention openings in the form of holes situated at the same radial distance from the seed metering shaft. The singulating disc constitutes, or provides, a wall that forms a barrier, i.e., a partition or delimitation, between two areas distributed on the respective sides of the disc. One of the areas communicates with a pressure-actuating device in the form of a fan for providing a positive pressure, wherein normal pressure prevails in the other area. By means of the pressure difference, the disc sucks fast a seed in each hole. In the rotation of the disc, each hole passes bristles or spikes the purpose of which is to pick away double seeds which may attach at some holes. At a defined location of the revolution of the disc, the pressure difference is put out of operation, the seed falling away and falling down into the drill furrow in the ground.
A limitation of the machine type described above is that each drill row has one singulating disc and consequently each row has one bin for seeds. Since the machines tend to become wider and wider, a machine gets many bins; there are machines with more than 30 bins for seeds. For a user, it is cumbersome and time-consuming to fill so many small bins.
DE 10 2006 010325, EP 598 636, U.S. Pat. No. 5,392,722, FR1503687, U.S. Pat. No. 5,231,940, U.S. Pat. No. 5,156,102 and U.S. Pat. No. 3,885,704 disclose planters embracing a seed metering device comprising a seed element in the form of a drum, which forms a cylindrical casing and which is rotatable around a concentric seed metering shaft. The casing is provided with through retention openings in the form of holes distributed in a plurality of arrays distributed along the seed metering shaft, each one of which extends in the circumferential direction of the casing. The drum constitutes, or provides, a wall that forms a barrier between two areas distributed inside and outside, respectively, the casing. The area outside the drum communicates with a fan for providing a positive pressure, wherein normal pressure prevails inside the casing. By means of the pressure difference, the drum sucks fast a seed in each hole. In an area through which the holes pass and in which a decrease of the pressure difference is accomplished, e.g., by means of a special roll or a separating flexible wall, the seeds are released as they are brought through the area. From the drum, the seeds are conveyed from each hole array by air through a respective line to a respective seed nozzle, which mouths directly in or above a drill furrow, which most often is opened by two inclined discs.
Such a drummed planter has the advantage that a drum and a seed bin serve a plurality of drill rows. This means that a machine having many drill rows still can have few bins.
Common to the two main types of planters, i.e., with singulating disc and drum, respectively, is that pneumatics is utilized for several purposes. On one hand, the transportation of seeds from the central bin takes place pneumatically, and on the other hand pneumatics is utilized for the seed metering process.
Additional examples of devices that relate to seed metering are disclosed in EP 0141638, U.S. Pat. No. 5,799,598, U.S. Pat. No. 4,898,108, U.S. Pat. No. 4,091,964, U.S. Pat. No. 4,026,437 and U.S. Pat. No. 3,156,201.
A problem of positive pressure systems, irrespective of whether it is about sow housings having plane seed discs or seed drums, is the high power requirement of the fan system, which often is hydraulically driven. Together with other hydraulics of these sowing machines, the power requirement of the hydraulic system is often so high that the capacity of a common standard tractor is not always sufficient. This means that the capacity of the tractor has to be specified before the manufacture of the same, and in other words be bought simultaneously with the contemplated sowing machine.
A great part of the power loss that arises in a sow housing having positive pressure over a seed element such as a seed disc or a seed drum is the air leakage that arises in the holes of the seed element that do not contain seed. This is the case for the holes of the seed element that are in the sector that lies between the area where seeds clear from the seed element and the seed reception area of the seed element where the holes are filled with seeds.
The object of the present invention is to eliminate or at least reduce the power loss that arises because of air leakage through the holes of the seed element.